Abstract The meniscus plays a vital role in healthy knee function. However, given the centrality of this tissue in load transfer and the demanding physical environment, injury is common and healing in adults is limited. The current lack of regenerative solutions for knee meniscus injury arises, in part, from the significant gap in our understanding of the cellular origins and regulation of meniscus tissue during development. While it is well appreciated that the meniscus arises from a specialized progenitor cell population that first defines the forming synovial joint (interzone cells), the regulation and timing of the differentiation of these cells, their phenotypic heterogeneity, the type and timing of matrix that these cells produce within defined intervals, how this matrix matures and feeds back to influence cell function and fate, and the role of active mechanical forces (that begin during the first stages of joint motion), remain poorly understood. To address these limitations, this proposal uses a series of novel mouse models and micro-scale experimental techniques to investigate the origin and track the fate and function of cells that comprise the mature meniscus. We will also define the time-evolving structural and mechanical features of the developing matrix, and query the role of joint loading and cellular response to mechanical inputs in this developmental paradigm. Our central hypothesis is that a common pool of meniscal progenitor cells arises from the interzone, that these cells are acted on by microenvironmental cues defined by early matrix assembly and active mechanical signals (that arise with joint loading), and that these inputs act together to refine and direct meniscus maturation, enabling its adult function.